Bruce Bennett/Getty ImagesRyan McDonagh #27 celebrates their 3 to 0 win over the New Jersey Devils with teammate Brandon Prust.

NEW YORK — In professional sports, every injury to a key player provides an opportunity for some other player to step into a greater role. It’s rare, though, when the player stepping up into the key role makes the injury turn out to be a good thing for his team.

When first-pair defenseman Marc Staal was unable to start the season for the Rangers because of the lingering effects of a concussion he’d suffered last February, Rangers coach John Tortorella decided to plug Ryan McDonagh into Staal’s spot on the first unit, next to veteran Dan Girardi.

“It’s funny how it works out when you end up with injuries,” Tortorella said Tuesday before the Rangers’ practice at Madison Square Garden. ”We always talk about when there’s injuries, another guy gets an opportunity. You never know where it’s going to lead you.”

Where it led the Rangers was a 3-0 victory that gave them a 1-0 lead in the best-of-seven series. Both McDonagh and Girardi played starring roles in the game — Girardi scored the game’s first goal 57 seconds into the third period, walking into a soft pass by rookie Chris Kreider and blasting a one-time slapshot past Devils goalie Martin Brodeur, while McDonagh made two standout defensive plays — racing from behind to catch up to Devils stars Zach Parise and Ilya Kovalchuk on separate breakaways, and helping thwart both scoring chances.

In the case of Parise, McDonagh — a first-round pick by Montreal who was traded to the Rangers in the Scott Gomez deal in 2009 — caught the Devils’ captain from behind, got a body on him, and prevented him from getting a shot off at Rangers goalie Henrik Lundqvist. On Kovalchuk, the 22-year-old McDonagh was able to cut off the Russian’s angle to the middle of the ice, forcing him to instead settle for a weak backhand shot that Lundqvist saved.

“Obviously, you’re not trying to be behind guys and give them breaks like that,”
McDonagh said. ”But when it happens, you want to be smart and try not to take a penalty if you can do that. You always want to be moving your legs all the way back. You never know, it might be one stride that can get you back in time.”

Staal missed the first 36 games of the season before returning in the Winter Classic game against the Flyers on Jan. 1. In the time he was away, Girardi and McDonagh melded so well that Girardi made the All-Star team for the first time in his career and Tortorella kept the pair together even after Staal returned.

“I’m not sure if I’ll ever split those two guys up,” Tortorella said of Girardi and McDonagh. ”That’s just the way it works, and that’s the interesting part when you have injuries, how things work out.”